Greyscale Dithered Film 300 x 450
DITHERED GREYSCALE FILM
Maximum Image: 280 x 430mm
This is a polyester photographic film greyscale , created using a stochastic dithered effect that is often used in high resolution imaging technologies.
A greyscale halftone image is one where each pixel in the image represents a different rate of grey intensity. The general consensus is to use a range where 0% - totally clear and 100% is totally black. Our process is a binary one, whereby we can only image "black" pixels on clear film, so we cannot create a normal greyscale image as defined by "photography". However, we have a solution that works in the vast majority of cases, and that is pixelation or dithering to create a halftone.
The dithering process is one where each tone of grey is represented via a density of pixels - the size of the pixel does not change - it is the density that changes. So a low density in a specific area will give tones such as 5% and 10%, where a high concentration or density of pixels will give a high tone such as 80% or 90%. At the mid point of 50%, there will be an equal number of dark and clear pixels. By creating a dithered pattern - part of the process is to make the pixel that creates the "grey" smaller than the lens (or eye) can resolve. In this manner, the lens will just see an overall grey tone rather than individual pixels.
DIFFERENCE BETWEEN HALFTONES AND DITHERING
The halftone process uses dots of differing sizes (pulse-width modulation) and spacing (frequency modulation) to represent the required grey level. Smaller pixels for low tones, bigger pixels for mid tones.
The dithering process uses the same size pixel everywhere, but it is the number of pixels (the concentration, or density, over a given area) that represents the grey tone. Fewer dark pixels for low tones and more dark pixels for high tones.
PIXEL AND RESOLUTION
The higher the pixel resolution of a source file, then the smaller the actual pixel size, which translates to the greater the detail that can be reproduced. We have 4 standard resolutions that can be chosen, although you are free to choose any other resolution if you need a specific spatial frequency.
Below are guides to pixel sizes dependant on the resolution chosen, and most importantl the maximum possible image area that can be reproduced. The pixel count affects the file size, and we are limited to 2GB data files after processing, so the most important factor is to choose a resolution that is allows the physical size of pattern that you requir.
|Resolution||Pixel Size||Maximum Image Area|
|1000 dpi||25um||6400 cm2|
|5000 dpi||5 um||256 cm2|
Please tell us what format you will be sending. Data formats listed above are only a small section of what is available. If your chosen format is not listed, please contact us for further information and clarification. We are also able to provide a full drafting service whereby we can create your designs from drawings and descriptions.
Films are normally referred to as Clearfield (positive) & Darkfield (negative)
Positive means that the data you have supplied Black on the film, with the background being clear film.
Negative is the opposite of this, where the image supplied will be inversed and the picture will be clear and the background will be black.
Our standard production turnaround is 3-4 days from receipt of the artwork, purchase order and related documents. We generally send checkplots with every order, and it is vital that these are replied to within a short delay in order that we can meet the schedule required. The production schedule assumes the original data package is correct and does not need to undergo revisions or changes. For large volume orders, or large photomasks on high resolutions, please enquire before ordering premium services.
Standard (5 days) : This is our standard service, and whilst we get 99% of orders shipped within this period, these are guidelines only and may change in periods of high demand. Where data packages are good, and all paperwork is completed promptly, we can often ship early.
Premium (2 Days ) : A premium service. A complete manufacturing package (data/instructions/order) must be with us by no later than 11.00am.
YOUR DRAWING NUMBER
Please let us know the CAD file name / number so that we can tie together the uploaded data and the order.
Here you can inform us of any other requirements or specifications regarding the order.
Please see the TECHNICAL sections, DOWNLOAD sections and FAQ for further information. If you still require clarification, please either email or click for LIVE SUPPORT.
Polyester Film is a typical substrate used in the photographic process, and forms the most common substrate in applications that involve general multiple exposures (such as PCBs, etching, printing etc.). Polyester is excellent due to its low-cost nature, but must be handled carefully and used in controlled environments if dimensional accuracy is required.
Films used for photo-masks have the following component layers: a plastic base, a photosensitive emulsion layer (silver halide) and a backing layer.
This plastic base is polyester material, and has a thickness of 0.18 mm. The emulsion layer is composed of gelatine and silver halide and other chemicals, which adds another 0.005mm in total.
When we expose the film in the imager, the light energy from the laser interacts with the silver halide crystals suspended in the coated gelatine layers. Development, a chemical process, converts exposed silver halide grains into metallic silver. The next step in the chemical process is fixation. The fixer stops development and removes the unexposed silver halide grains in non-image areas. Finally, the film is washed/dried/cleaned and inspected.
The final result is a ‘black’ image coated on one side of the polyester base. The density of the film is very high, typically Dlog of 4.5 – 5, giving it an excellent opacity to all common light sources.
Two concerns with emulsion film over glass are stability and robustness. Both the polyester and the gelatine absorb moisture and heat from their surroundings, and as such they undergo dimensional changes – quite considerably for some large area films. The other problem with the Gelatine/Emulsion is that it is relatively soft and must be handled carefully to avoid damage and scratches.
Q: What is the smallest feature that you can do ?
A: This depends upon the resolution that we image at, the material that we use, the tone of the film, and most importantly the feature type (Spot, square, line etc). This all makes it very hard to give a figure, but as a very rough guide we can make down to 5=6um
Q: What resolution should i pick ?
A: The higher the resolution, then the sharper the edges of the features, the smaller the features possible, the more accurate the features will be, the sharper the corners in of the features, and also the smoother the circles. Some customers will notice this difference straight away, some will hardly notice any difference. Every customer has different requirements and different priorities. If in doubt, chose a higher resolution to ensure your requirements are met, but we are happy to advise if you send us your database.
Q: What does the term POLARITY mean ?
A: Polarity is the tone of the film, and in layman's terms it is what you might call Positive and Negative. When you draw your design on your computer, you need to decide if the objects that you draw are going to be opaque on the film- and therefore to block the light - or transparent areas on the film. It's best to always think of the data that you draw either being positive data, or negative data.
Q: I've designed my image with the wrong polarity - what do i do ?
A: We can use the original design file and simply reverse the tone of the mask. This is much easier than supplying new data.